The authors showed that the " 'normal prion protein' in the brains of living mice can be converted into different forms depending on the type of abnormal human prion that initiated the conversion. The result is different patterns of pathological changes in the host, as would be expected for different prion strains." Prusiner proposed that "infection with one of the misfolded proteins can induce disease by forcing healthy PrP molecules to refold themselves into abnormal prions." 

(Order of authorship in the original publication: Telling, Parchi De Armond...Prusiner.)

(Thanks to Juan Weiss for this reference and its interpretation.)